Nearly 90 per cent of respondents raised concerns at being required to take on HR functions as part of the plans.

EIS general secretary Larry Flanagan said: “These proposals could radically change the job of head teacher, creating additional bureaucratic and managerialist tasks on top of an already severe workload burden.

“The EIS is supportive of the idea of headteachers being the leader of learning, but they require the time and resources to do this effectively.”

Secondary headteachers’ union School Leaders Scotland welcomed the idea of further powers but warned a salary increase would need to reflect the additional responsibilities.

Yesterday, local authorities representative body COSLA warned the plans meant individual teachers could be sued and would need to seek out their own legal advice independently of councils.

Dave Watson, UNISON’s head of policy and public affairs, said taking HR and procurement powers away from councils would remove democratic accountability.

“It is very clear that the key problems in Scottish education are not caused by a lack of power for headteachers – it is budget cuts, a teacher shortage and loss of support staff,” he said.

“The government must put its focus on children, not structures, and provide the much needed funding in education and wider local government services that support children and families.”

Ross Greer, education spokesperson for the Scottish Greens, said focus groups had also revealed a lack of support for the headteacher’s charter.

“In a focus group of sixteen headteachers this week every one told me that they oppose this charter,” he said.

“What headteachers need is more staff in their schools, more resources and more time to give our children and young people the education they deserve.”

A Scottish Government spokesperson said the reforms are “based on international evidence of how high-performing education systems work and will deliver extra help for teachers in the classroom, more professional development and a stronger voice for parents and pupils”.